Spray coating of a liquid or hot melt in a wide band on a wide and continuously moving substrate or web is required in many industrial fields. For the production of paper diapers, for example, an adhesive is spray coated in a wide band on a long water-impermeable sheet which is wide and fed continously. This lined sheet is adhered to a water-absorbing pad made of a long nonwoven fabric which is also fed continuously. This product is then cut, assembled as one paper diaper, and shipped to the market.
The following examples are the principal methods and apparatus employed in the past for the spraying of an adhesive or coating agent, i.e., a liquid or hot melt material, in a wide band. In the first example, a liquid or hot melt material is sprayed in flat fan form from a nozzle in an airless manner, using a special nozzle as shown in Japanese Kokoku No. 61[1986]-50,655. In the second example, a special nozzle as shown in Japanese Kokai No. 62[1987]-204,873, is used to spray the material in a flat fan form while causing auxiliary air to impinge upon the material as it is ejected from the nozzle. If the third example, while spraying the material from a long and narrow slot nozzle, the sprayed material is contacted by air ejected from a similarly long and narrow slot nozzle, as shown in Japanese Kokai No. 6[1994]-170,308.
In the first and second of these examples, the distribution density of the sprayed material varies between the center section and the two edge sections of the fan-shaped wide spray pattern. The density of sprayed material is higher at the center than at the two edges. Furthermore, when the sprayed material hits the web, the jet stream closer to the two edges of the fan shape strikes at an inclined angle, and thus rebounds easily, compared to the material at the center. As a result, there is variation in amount that sticks at the center compared to the two edges of the fan shape.
In the third example, the material path in the slot nozzle body must widen after leaving the entrance port, in order to eject the liquid or hot melt material in a wide band from the slot nozzle. Various existing devices have been engineered so as to allow the material to flow uniformly over the entire region of the slot nozzle width. Such devices include a so-called coat hanger die widened to a triangle, or finely dividing the slot width into sections and providing each section with a metering gear pump to measure the quantity. While these devices can be used to achieve a uniform material stream of high accuracy across the entire die width, it is sometimes difficult to precisely quanitfy the amount of material which is delivered across the volume of the nozzle.
It is an object of the present invention to provide methods and apparatus for spraying a liquid or hot melt material in a wide band with uniform distribution and high accuracy over the entire region in the width direction.
It is another object of the present invention to facilitate the ability to precisely quantify the amount of liquid or hot melt material sprayed via such a system.